Django REST Serializer Method Writable Field

I'm reading up on Django REST Framework and I have a model that is serialized with getters using the SerializerMethodField().

However, when I POST to this endpoint, I want to be able to set this field as well, but that doesn't work because, as the docs show above, you can't write to a SerializerMethodField. Is there any way in Django REST to have a serializer field that you define a custom getter method for, and a custom setter method?

EDIT: Here's the source of what I'm trying to do. Client has a 1-to-1 relationship with User.